Polyphenylene ether resins have been known to be very useful engineering plastic materials because of their good mechanical properties, electric properties and thermal resistance. Electric machines and appliances used at home have been strongly required to have high flame retardancy in order to prevent an accident such as a fire and an electric shock caused thereby. According to an increasing demand for electric machines and appliances, the demand for plastic materials used in this field having a high flame retardancy also has been increasing.
Various methods for imparting a flame retardant property to a polyphenylene ether resin have been proposed. For example, there have been proposed methods for adding halogen compounds or phosphorus compounds such as a phosphate ester. However, a halogen compound generates fumes or a corrosive hydrogen halide in a molding process, and in some cases causes problems of toxicity and to the environment. Moreover, the conventionally proposed methods disadvantageously deteriorate the impact resistance and high heat deflection temperature inherent in a polyphenylene ether resin.
It is known that the addition of an aromatic phosphate ester imparts an efficient self-extinguishing property to a resin composition. Such a self-extinguishing resin composition, however, often has been disqualified at V-0 or V-1 in the UL94 burning test because of dripping from a specimen during or after burning or luminous burning thereof. Even a resin composition which satisfies the V-0 level, can be disqualified at the 5V level of UL94 test, i.e., a plaque test.
It is known that a composition with flame retardancy and anti-dripping properties can be obtained by adding polytetrafluoroethylene resin (which will hereinafter be abbreviated as “PTFE”) to a polyphenylene ether resin as described in U.S. Pat. Nos. 4,107,232 and 4,332,714 and JP-A-59-98158 (the term “JP-A” used herein means an unexamined Japanese patent publication”). PTFE is known to provide great improvement in the anti-dripping properties and friction properties of a thermoplastic resin by it being added in a small amount to the thermoplastic resin.
Generally, when PTFE is added to a thermoplastic resin, both are kneaded at a temperature lower than the melting point of PTFE, since the melting point of PTFE is higher than the processing temperature of the thermoplastic resin. PTFE is easily fiberized or agglomerated by the shearing forces created. Therefore, the PTFE kneaded into the thermoplastic resin is fiberized and forms a network therein so that effects such as anti-dripping properties are exhibited. However, that PTFE is easy to fiberize or agglomerate makes the handling of PTFE difficult, and various methods for improving the handling thereof have been proposed. For example, JP-A-10-30046 discloses a method comprising treating the PTFE with a dispersant agent such as a higher fatty acid before use.
PTFE usually has a powdery form, and therefore, if it used in the form of powder, it disperses and pollutes working areas. When it is mixed with a thermoplastic resin or fed to an extruder, PTFE causes, as a result of its above-mentioned properties, a blocking phenomenon wherein the PTFE agglomerates and adheres to the wall of a feeding apparatus or an extruder which makes stable feeding and kneading difficult, and clogs a filter located at the die head of the extruder and obstructs extrusion. When a resin composition obtained thereby is molded, the resultant molded article often has agglomerates of PTFE on its surface because of the poor dispersibility of the PTFE, causing problems such as deterioration of its impact resistance.
On the other hand, in order to improve the handling of PTFE, investigation of pelletized compositions containing PTFE at a high concentration has been made and such a granular PTFE composition has been disclosed in various documents such as JP-A-9-324124, JP-A-9-324071, JP-A-9-324072, JP-A-9-324073, JP-A-9-324074, JP-A-9-324092 and JP-A-9-324093. However, the PTFE disclosed in these documents does not have enough dispersibility, and is difficult to extrusion knead for a long time and it inhibits performance of the resin composition.
As described above, the prior art for imparting flame retardancy to a polyphenylene ether resin has problems such difficulty in handling and insufficient flame retardancy. Moreover, PTFE used to inhibit dripping upon burning has many problems in physical properties such as poor handling property and adhesion to processing apparatus. Thus, improvement has been required.